Field of the Invention
The present invention relates generally to a method for protecting a layer, including a method for capping a doped layer to block diffusion of dopants, by forming a hydrocarbon-based extremely thin film by plasma-enhanced atomic layer deposition (PEALD).
Related Art
A SiN film can be formed by plasma-enhanced atomic layer deposition (PEALD) at a temperature of 400° C. or less without causing chemical or physical damage to an underlying layer, and thus, application of the film as an impurity-dispersion blocking film, a pore-seal film for low-k dielectric film, and a protective film for next-generation memory devices has been studied. However, as the size of semiconductor devices has been reduced, further thinning of these films is in demand. Also, since lowering the process temperature is in demand, it becomes more difficult to obtain films having sufficient chemical resistance and barrier properties.
For example, a dopant thin film such as a doped silicon oxide film (e.g., borosilicate glass (BSG) and phosphosilicate glass (PSG) film) can be deposited by an ALD process as a solid state diffusion or solid state doping (SSD) layer over a semiconductor substrate in a structure such as a FinFET structure. However, as illustrated in (a) in FIG. 2 (which is a schematic representation indicating a schematic cross sections of a partially fabricated integrated circuit according to a comparative example), when a dopant thin film 26 deposited on a silicon substrate 25 is exposed, dopant elements 28 such as B and P are dissociated from the dopant thin film 26 with time (referred to as aging) during storage and/or during a subsequent annealing process, and as a result, in a subsequent annealing process, sufficient dopant elements do not diffuse to the substrate. Thus, in order to prevent the aging of dopant elements from a dopant thin film, as illustrated in (b) in FIG. 2 (which is a schematic representation indicating a schematic cross sections of a partially fabricated integrated circuit according to a comparative example), a cap film 27 is deposited on top of the dopant thin film 26 as a dispersion blocking film. As the cap film 27, non-doped silicon glass, SiN film, or SiO film is typically used. However, although dispersion of dopant elements can be suppressed by the formation of the cap film, chemical resistance of the cap film is degraded, i.e., wet etch rate becomes high, when the dopant concentration in the dopant thin film is high, as illustrated in FIG. 3 which is a schematic representation indicating a schematic cross section of a partially fabricated integrated circuit after etching according to a comparative example, showing that layers 32c on sidewalls of a substrate 33 enclosed by dotted circles are thinner than layers 32a, 32b on top and bottom.
In order to manage the above problems, by increasing the thickness of the dopant thin film so as to increase the concentration of dopant elements in the dopant thin film, it may be possible to increase the amount of dopant elements to be diffused to the substrate. Also, by increasing the thickness of the cap film so as to block dispersion of the dopant elements to a higher degree, it may be possible to increase the amount of dopant elements to be diffused to the substrate. However, the increase of thickness of the dopant thin film or the increase of thickness of the cap film may interfere with the standard fabrication processes.
The above discussion of problems and solutions and any other discussions disclosed in this disclosure in relation to the related art has been included solely for the purposes of providing a context for the present invention, and should not be taken as an admission that any or all of the discussion was known at the time the invention was made.